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The United States Environmental Protection Agency (“EPA”) announced it is initiating a new review of the Ozone National Ambient Air Quality Standard (“NAAQS”).
EPA states it is taking this action based on advice provided by the Independent Clean Air Scientific Advisory Committee (“CASAC”).
The Clean Air Act requires that EPA establish ambient air quality standards (i.e., National Ambient Air Quality Standards [NAAQS]) for a limited number of air pollutants. Ozone is one of the air pollutants currently designated as a Clean Air Act criteria air pollutant for which EPA set a NAAQS. It is an irritant gas not emitted by any particular source and therefore is a secondary air pollutant. Ozone is formed in the atmosphere in the presence of sunlight and heat from other precursor air pollutants including nitrogen oxide and hydrocarbons.
As a result of this designation as a criteria air pollutant, EPA many years ago set a NAAQS for the pollutant. The federal agency has an obligation pursuant to the Clean Air Act to review the NAAQS for each criteria air pollutant on a set periodic basis to determine, based on current science and studies, whether the standard should be strengthened.
When a NAAQS is established or revised, the states are then required to develop plans to ensure that their air quality regions meet this ambient standard. Each state is required to formulate, subject to EPA approval, an implementation plan (i.e., SIP) designed to achieve each NAAQS. The SIPs contain the measures and actions the state proposes to undertake to attain each NAAQS. These measures or actions must be enforceable through state regulations and typically include emission limits applicable to certain types of stationary sources.
The states are somewhat free to make their own choices as to how they will attain the NAAQS through their SIPs. However, the SIP and subsequent revisions must be reviewed and approved by EPA for determination that certain criteria set forth in Section 110 of the Clean Air Act have been met.
EPA Administrator Michael S. Regan stated in an August 18th letter to the Chair of the CASAC that it was responding to their June 9th letter conveying its comments on the federal agency’s:
Policy Assessment for the Reconsideration of the Ozone National Ambient Air Quality Standards, External Review Draft Version 2.
The Administrator noted that he had previously determined in 2021 that EPA would reconsider a 2020 ozone NAAQS decision undertaken during the Trump Administration.
Administrator Regan further noted that:
. . . In light of CASAC’s significant comments on the draft policy assessment and its advice on the importance of new studies not evaluated in the 2020 Integrated Science Assessment, it is clear that CASAC’s careful review has identified several issues arising in the reconsideration that warrant additional evaluation and review, both by the EPA and by CASAC, including newly available information that has not yet been integrated into the air quality criteria and the value of developing additional analyses to inform further evaluation of the current standards.
The August 18th letter further states that the Administrator has instructed EPA staff to immediately initiate a new review of the ozone NAAQS as well as the underlying air quality criteria.
A copy of the following three documents can be downloaded below:
